An organic light emitting device is a device in which a thin film containing a fluorescent organic compound or a phosphorescent organic compound is interposed between an anode and a cathode; excitons of the fluorescent compound or the phosphorescent compound are generated by injection of electrons and holes from the electrodes and a light radiated when the excitons return to the ground state is utilized.
In a research by Eastman Kodak Company in 1987 (non-patent document 1), there is reported a light emission of about 1,000 cd/m2 at an applied voltage of about 10 V for a device of functionally separated two-layer structure using ITO for an anode and a magnesium/silver alloy for a cathode, respectively, an aluminium-quinolinol complex as an electron-transporting material and a light emitting material and a triphenylamine derivative as a hole transporting material. Related patents include patent documents 1 to 3.
In addition, light emission of from ultraviolet region to infrared region is possible by changing the type of the fluorescent organic compound and researches of various compounds have been conducted actively recently. For example, they are described in patent documents 4 to 11.
In recent years, there have been a number of studies in which phosphorescent compounds are used as a light emitting material and an energy in a triplet state is used for an EL (electro luminescent) emission. A group of Princeton University has reported that an organic light emitting device using an iridium complex as a light emitting material exhibits a high light emission efficiency (non-patent document 2).
Moreover, a group of Cambridge University has reported (non-patent document 3) an organic light emitting device using a conjugated polymer other than the organic light emitting device using the low-molecular materials as described above. In this report light emission in a monolayer is confirmed by forming a film of polyphenylenevinylene (PPV) in a coating system.
Related patents on organic light emitting devices using conjugated polymers include patent documents 12 to 16.
Thus, recent progress in organic light emitting devices is remarkable, and possibilities for a wide range of applications are indicated since it is characterized in that a thin and lightweight light emitting device having a high luminance at a low applied-voltage, diversity of light emitting wavelength and high-speed response can be prepared.
However, a higher-luminance light output or high conversion efficiency is required under present circumstances. In addition, there are numbers of problems in terms of durability such as variation with the elapse of time during use for a long period of time and the deterioration due to an atmospheric gas including oxygen or humidity. Moreover, the light emission of blue, green and red having a good color purity is required for applications such as a full-color display, but these issues are not sufficiently satisfied.
On the other hand, phenanthroline compounds are used as an electron transporting material or a light emitting material by the excellent electron transporting property thereof. Examples of documents in which the phenanthroline compounds are reported to be used for an organic light emitting device include patent references 17 to 21, but their properties when they are used as a light emitting material or an electron transporting material are not sufficient.
[Patent Document 1]
U.S. Pat. No. 4,539,507
[Patent Document 2]
U.S. Pat. No. 4,720,432
[Patent Document 3]
U.S. Pat. No. 4,885,211
[Patent Document 4]
U.S. Pat. No. 5,151,629
[Patent Document 5]
U.S. Pat. No. 5,409,783
[Patent Document 6]
U.S. Pat. No. 5,382,477
[Patent Document 7]
U.S. Pat. No. 5,130,603; U.S. Pat. No. 6,093,864
[Patent Document 8]
U.S. Pat. No. 5,227,252
[Patent Document 9]
Japanese Patent Application Laid-Open No. H5-202356 (no corresponding foreign document)
[Patent Document 10]
Japanese Patent Application Laid-Open No. H9-202878 (no corresponding foreign document)
[Patent Document 11]
Japanese Patent Application Laid-Open No. H9-227576 (no corresponding foreign document)
[Patent Document 12]
U.S. Pat. No. 5,247,190
[Patent Document 13]
U.S. Pat. No. 5,514,878
[Patent Document 14]
U.S. Pat. No. 5,672,678
[Patent Document 15]
U.S. Pat. No. 5,317,169; U.S. Pat. No. 5,726,457
[Patent Document 16]
Japanese Patent Application Laid-Open No. H5-247460 (no corresponding foreign document)
[Patent Document 17]
U.S. Pat. No. 5,393,614
[Patent Document 18]
Japanese Patent Application Laid-Open No. H7-82551 (no corresponding foreign document)
[Patent Document 19]
U.S. Pat. No. 6,010,796
[Patent Document 20]
Japanese Patent Application Laid-Open No. 2001-267080 (no corresponding foreign document)
[Patent Document 21]
Japanese Patent Application Laid-Open No. 2001-131174 (no corresponding foreign document)
[Non-Patent Document 1]
Appl. Phys. Lett. 51, 913 (1987)
[Non-Patent Document 2]
Nature, 395, 151 (1998)
[Non-Patent Document 3]
Nature, 347, 539 (1990)